A common malfunction with Replica '66's, and '73's:
“The 66-73 jam.” Usually a split case allows the bullet to retract into the case, making the overall length too short and locking up the gun. The next round slid halfway into the carrier preventing its lifting.
Insert the screw knife tip into the carrier in between the two rounds and…
…push the “next” round toward the muzzle until it is in the magazine tube again, freeing the action.
Close the bolt, sliding the knife out as you do so.
Extract the bad round from the loading gate. Sometimes the rounds pop out easily. Sometimes pushing the round forward with the screw knife and releasing will allow it to pop out. Then work the lever to load the next round. FRONT SIGHT! Resume firing. Remember to load a fresh round to replace the bad round.
Thanks to Redwing for his help with these photographs.
Do note that due to the restrictions of making still pictures of this process, that the hand positions and such are not necessarily the most efficient for doing this quickly. Practice it until you're blue in the face, then do it some more, and you'll come up with a method that is efficient for you.